Translocation

Question 1

Explain the ways sucrose enters sieve tube elements in Mass flow theory

Answer 1

.Directly into sieve tubes via the symplast route through plasmodesmata
.Active transport through companion cells into the sieve tubes
.Cotransport of H+/sucrose
.H+ actively pumped out of companion cells into the leaf cell – creates a concentration gradient between outside and inside of companion cell membrane
.A co-transport protein can transport H+ and sucrose simultaneously. When both are bound, the configuration changes, and the protein opens to the membrane interior, releasing H+ and sucrose into the companion cell. The sucrose diffuses out of the companion cell into the sieve tube.